When fuel is burned to create an expanding gas, and the forces generated thereby are utilised to rotate a turbine, or to drive a piston, which in turn rotates a crankshaft, a situation called overspeed can develop. It is then necessary to obviate the flow of fuel to the combustion zone as quickly as possible, so as to avoid mechanical damage to the associated powerplant. This means that it is desirable to provide fuel shut off capability which will satisfy both normal and abnormal running speeds of the apparatus being driven.
It is known, to take a plurality of tappings from the high pressure fuel system, and provide each tapping with an outlet and a dedicated blocking device, with which to selectively block the outlet as and when appropriate. This is in order to achieve the fuel flow control as described hereinbefore, so as to protect the associated driven apparatus. It is an object of the present invention to provide an improved fuel flow control apparatus.